Imparting flame-resistance to polyurethane foams based on polyether polyols and polyester polyols has been a long-sought goal. Various phosphoric acid esters or metal oxides may be used for this purpose. In GB-A 2,168,706, expandable graphite is proposed as a flame-retardant for polyurethane ("PUR") ether foams. Such use of expandable graphite was found, however, to have the following disadvantages:
powerful wick action by the graphite component which causes burning to continue, PA1 heavy formation of fly ash and the formation of soot which in part continues to glow, and PA1 formation of finely powdered cinder which is very easily dissipated. PA1 no wick action due to the addition of graphite, PA1 no formation of fly ash, and PA1 no powdery combustion residue. PA1 a) from 1 to 30 parts by weight, based on component 2), preferably 1 to 20 parts by weight and most preferably 2.5 to 15 parts by weight, of graphite which has been modified with inorganic expandable materials, wherein said expandable graphite is used either alone or, preferably, in combination with PA1 b) from 1 to 30 parts by weight, based on component 2), preferably from 1 to 25 parts by weight and most preferably from 2.5 to 20 parts by weight, of an inorganic co-flame-retardant. PA1 a sulfate-containing expandable graphite having a sulfate content of from 1 to 40%, preferably from 1 to 30%, most preferably from 5 to 20%, PA1 ammonium polyphosphate as co-flame-retardant, PA1 calcium cyanamide as a co-flame-retardant, PA1 aluminum hydroxide as a co-flame-retardant, and PA1 calcium carbonate as a co-flame-retardant.
It was surprisingly found that when expandable graphite was used as flame retardant in PUR ester foams, the above disadvantages, which prevent the use of this flame retardant for technical processes, do not occur.
In a comparison test, ester foams according to this invention were used instead of the ether foams described in GB-A 2,168,706. Exposure of these ester foams to flames produces the following results, both when expanded graphite is used alone and especially when it is used in combination with inorganic flame retardant additives:
Instead, a heavily carbonizing, self-extinguishing, non-dripping foam is obtained. This result is confirmed by numerous conventional standard tests for flame retardants, such as BS 5852, Part 2, Crib 5 test: DIN 4102: MVSS: and UL 94.